Zanamivir (Relenza) is an antiviral medicine - a neuraminidase inhibitor, that is indicated for the treatment and prophylaxis of influenza viruses A and B.

• Zanamivir (Relenza) Prophylaxis:

  • It is used for the prophylactic treatment of influenza in adults and children older than 5 years of age.

• Zanamivir (Relenza) Treatment:

  • It is indicated for the treatment of uncomplicated acute illness that is caused by influenza A and B virus in adults and children 7 years and older who have been symptomatic for no more than 2 days.

  • The Advisory Committee on Immunization Practices (ACIP) recommends treatment for the following group of patients:

    • Severe, complicated, or progressive influenza illness

    • Those hospitalized

    • Individuals who are at higher risk for complications:

      • Children less than 2 years of age (highest risk is in children less than 6 months of age)

      • Adults 65 years of age or older

      • Individuals with chronic respiratory or cardiovascular conditions like asthma, hypertension, and CCF.

      • Individuals with chronic major systemic diseases like diabetes mellitus, liver disease, kidney dysfunction, blood disorders including sickle cell disease, or immunosuppression (including those caused by medications or HIV infection)

      • Persons with the central nervous system or neuromuscular conditions (including spinal cord injuries, stroke, seizure disorders, cerebral palsy, mental retardation, muscular dystrophy, or moderate to severe developmental delay which may compromise respiratory function, respiratory secretions, or increase the risk of aspiration pneumonitis.

      • Pregnant and postpartum women (2 weeks or less after delivery)

      • Individuals less than 19 years of age who are on long-term aspirin therapy

      • American Indians and Alaskan Natives

      • Morbidly obese (BMI ≥40) individuals

      • Residents of nursing homes or other such facilities

  • It may also be used in suspected or confirmed cases who were previously healthy (within 48 hours of clinical suspicion).

• Prophylactic zanamivir may be considered for the following individuals as per the ACIP guidelines:

  • Postexposure prophylactic treatment may be considered for unvaccinated family members or close contacts of suspected or confirmed influenza cases and individuals at high risk of influenza complications

  • Postexposure prophylactic treatment may be considered for healthcare workers who are not vaccinated and had occupational exposure without protective equipment.

  • Pre-exposure prophylaxis is only recommended for individuals who are at a very high risk of influenza complications and who cannot be protected at times of exposure.

  • Prophylactic treatment should also be administered to all the residents of institutions that house patients who are at a high risk to control outbreaks.

Zanamivir (Relenza) Dose in Adults

Zanamivir dose in the treatment of Influenza:

• Prophylaxis (household exposure):

  • Two inhalations (10 mg) once a day for seven days after the last known exposure.

• Prophylaxis (institutional outbreak):

  • Two inhalations (10 mg) once a day.
  • Treatment must be continued for 2 weeks or more and until about 7 days after the identification of the onset of illness in the last patient.
  • As per the CDC 2011 guidelines, Zanamivir should only be used to control institutional outbreaks of influenza if the virus is resistant to oseltamivir.

• Prophylaxis (community outbreak):

  • Two inhalations (10 mg) once a day.
  • Treatment should be continued until the activity of influenza in the community subsides or immunity is obtained from immunization.
  • Treatment may be continued for up to four weeks.

• Treatment:

  • Two inhalations (10 mg) two times a day for five days.
  • The first two doses on the first day should be administered at least 12 hours apart.
  • The subsequent days should be spaced about 12 hours.
  • Treatment should begin within 2 days of the onset of the clinical features.
  • Patients who are seriously ill may be advised a longer duration of therapy.

• Missed dose:

  • A double dose should never be administered.
  • If a dose is missed, it should be administered as soon as possible.
  • If the next dose is scheduled within 2 hours, do not administer the missed dose, continue the normal schedule.

Zanamivir (Relenza) Dose in Children

Note: 10 mg dose is provided by two inhalations (one 5 mg blister per inhalation):

Dose in the treatment of Influenza virus A and B:

• Children ≥7 years and Adolescents:
  • Two inhalations (10 mg) two times a day for 5 days
  • The initial doses on the first day should be separated by at least two hours.
  • Subsequently, the doses should be spaced by 12 hours.
  • Treatment should begin within two days of the development of the clinical features of influenza.
  • Patients who remain severely ill may be advised therapy for a longer duration.

Dose in the prophylaxis of Influenza virus A and B:

• Manufacturer's labeling:

  • Household setting: Children ≥5 years and Adolescents:

    • Two inhalations (10 mg) once a day for ten days.
    • Treatment should begin within 36 hours following the onset of signs or symptoms of the index case

  • Community outbreak: Adolescents:

    • Two inhalations (10 mg) once a day for four weeks beginning within five days of an influenza outbreak

  • Alternate dosing:

    • Children ≥5 years and Adolescents:

      • Household setting: CDC Recommendation:

        • Two inhalations (10 mg) once a day for seven days after the last known exposure.

      • Community outbreak: IDSA/PIDS recommendations:

        • Two inhalations (10 mg) once a day.
        • Treatment should be continued until the influenza activity in the community subsides or immunity is obtained from immunization
        • Treatment may be continued for up to four weeks.

      • Institutional outbreak: CDC recommendations:

        • Two inhalations (10 mg) once a day.
        • Treatment may be continued for 2 weeks or more and until about 7 days after the identification of the onset of illness in the last patient.
        • As per CDC 2012 guidelines, Zanamivir should be used to control institutional outbreaks of influenza if the influenza virus is resistant to oseltamivir.

      • HIV-exposed/-positive:

        • Two inhalations (10 mg) once a day for 10 days after the last known exposure.

Zanamivir Pregnancy Risk Factor: C

• Untreated influenza has been linked to adverse maternal and neonatal outcomes.
• The ACOG (American College of Gynecologists), 2018 report recommends that other neuraminidase inhibitors be used during pregnancy and for 2 weeks after birth.
• Zanamivir is not considered a preferred agent.

Zanamivir (Relenza) Dose in Renal Disease:

• Dose adjustment has not been provided by the manufacturer.
• However, the drug may get accumulated in patients with liver disease.

Zanamivir (Relenza) Dose in Liver Disease:

• Dose adjustment has not been provided by the manufacturer.

Common Side Effects of Zanamivir (Relenza) include:

• Central Nervous System:

  • Headache

• Gastrointestinal:

  • Sore Throat

• Infection:

  • Viral Infection

• Respiratory:

  • Nasal Signs And Symptoms
  • Tonsil Disease
  • Cough

Less Common Side Effects of Zanamivir (Relenza) include:

• Central Nervous System:

  • Chills
  • Fatigue
  • Malaise
  • Dizziness

• Dermatologic:

  • Urticaria

• Gastrointestinal:

  • Anorexia
  • Vomiting
  • Abdominal Pain
  • Decreased Appetite
  • Increased Appetite
  • Nausea
  • Diarrhea

• Neuromuscular & Skeletal:

  • Myalgia
  • Musculoskeletal Pain
  • Arthralgia
  • Rheumatic Disease

• Respiratory:

  • ENT Infection
  • Sinusitis
  • Bronchitis
  • Rhinitis

• Miscellaneous:

  • Fever

Contraindication to Zanamivir (Relenza) Include:

• Severe allergic reactions to zanamivir and any component of this formulation

Warnings and precautions

• Allergy reactions:

  • There have been reports of allergic reactions, including anaphylaxis and urticaria.
  • Treatment must be stopped immediately if an allergic reaction is detected.

• Events in neuropsychiatric:

  • Some patients may experience an abrupt onset of neuropsychiatric features such as confusion, hallucinations, and seizure.
  • Children are more susceptible to these events than adults, but it is impossible to establish a causal link.

• Respiratory effects

  • It can cause bronchospasm, which could be fatal.
  • Patients with allergic airway disease should avoid it and an effective bronchodilator that is quick-acting must be available.

• Respiratory disease

  • Patients suffering from chronic lung diseases such as asthma, COPD, and other respiratory conditions should not use it because they run the risk of precipitating their bronchospasm.
  • However, it should not be used in patients with such conditions.

Zanamivir: Drug Interaction

Monitoring parameters:

None required. 

How to administer Zanamivir (Relenza)?

Oral inhalation:

• It must be used with a Diskhaler delivery device.
• The foil blister disk that contains zanamivir powder for inhalation should not be manipulated, solubilized, or administered through a nebulizer.
• Patients on inhalational bronchodilators should use the inhalational bronchodilators prior to inhalational zanamivir.
• The dose should be administered preferably at the same time each day.

Mechanism of action of Zanamivir (Relenza):

• Zanamivir blocks the viral neuraminidase enzymes and can potentially alter the aggregation or release of the virus particles.

Absorption: Inhalation: Systemic: ~4% to 17%

Distribution: V : ~16 L

Protein binding, plasma: <10% is protein-bound.

Metabolism: It is not metaboolized.

Half-life elimination in the serum: 2.5 - 5.1 hours

Time to reach the peak plasma concentration: 1 - 2 hours

Excretion: Unabsorbed drug is excreted in the feces. In urine, it is excreted as unchanged drug.

International Brands of Zanamivir:

• Relenza Diskhaler
• Relenza
• Virenza

Zanamivir (Relenza) Brands in Pakistan: